Mechanisms

Question 1

Outline the 3 parts of free radical substitution

Answer 1

Initiation
Propagation
Termination

Question 2

What atoms are involved in free radical substitution?

Answer 2

Halogen atoms

Question 3

Outline the steps in initiation

Answer 3

Diatomic atoms gain one electron each to become 2 free radicals
e.g: Cl2 -> 2Cl*

Question 4

Outline the steps in propagation

Answer 4

1. One free radical reacts with reagent to form a new free radical from the compound
2. New free radical reacts with diatomic atoms to form OG free radical

Question 5

Outline the propagation of CH3CH2F + Cl2

Answer 5

1. CH3CH2F + Cl* -> CH3C*HF +HCl
2. CH3C* HF +Cl2 -> CH3CHFCl + Cl*

Question 6

Outline the steps of termination

Answer 6

All 3 combinations of free radicals cancel out

Question 7

Outline the 3 termination steps for CH3CH2F + Cl2

Answer 7

1. Cl* + Cl* -> Cl2
2. CH3C* HF + Cl* -> CH3CHClF
3. 2CH3C*HF -> CH3CHF - CHFCH3

Question 8

Outline the 3 Nucleophiles, their reagents and the conditions that undergo nucleophilic substitution

Answer 8

1. :OH- - KOH/NaOH (aq) - Reflux
2. :CN- - NaCN/KCN (aq) ethanol solvent - Reflux
3. :NH3 - NH3 - sealed tube

Question 9

Outline why Ammonia nucleophilic substitution is in a sealed tube

Answer 9

NH3 BP is low so reflux = evaporate

Question 10

Outline the mechanism steps for nucleophilic substitution with ammonia

Answer 10

1. NH3 bonds to C with Halogen - removes halogen atom
2. CNH3+ loses H atom from 2nd :NH3 atom to form NH4+
3. NH4+ forms NH4Br with :Br-

Question 11

Outline what atoms react in elimination

Answer 11

Halogenoalkane + KOH or H2SO4
Solvent = ethanol

Question 12

Outline the steps of elimination reactions

Answer 12

1. :OH- bonds with H on adjacent C to C with halogen - creates double bond & H2O
2. Halogen lost by saturated C - alkene formed

Question 13

Outline the 2 reactions of how CFCs reduce Ozone

Answer 13

1. Cl* + O3 -> ClO* + O2
2. ClO* + O3 -> Cl* + 2O2

Question 14

Define electrophiles

Answer 14

Electron pair acceptor

Question 15

Outline what reacts in electrophilic addition

Answer 15

Alkenes (or anything e- dense) and electrophiles

Question 16

Outline 3 electrophiles

Answer 16

1. Halogens (Br2, Cl2, etc)
2. HBr
3. H2SO4 (used in fermentation)

Question 17

Outline the steps in electrophilic addition

Answer 17

1. Electrophile accepts e- (+ dipole gains)
2. -ve Ion attacks + C atom

Question 18

Outline the structure of H2SO4 when drawing mechanisms

Answer 18

H—OSO3H

Question 19

Outline the electrophilic addition steps of fermentation

Answer 19

1. H+ accepts 2e- from C=C
2. :O-SO3H attacks C+ forming alkane
3. Warm H2O with H+ (aq) used - forms alcohol from alkane & reforms H2SO4

Question 20

Define a Carbocation

Answer 20

Ion with a + C atom

Question 21

Outline primary, secondary and tertiary carbocations

Answer 21

Primary = Only attached to 1 C group
Secondary = Attached to 2 C groups
Tertiary = Attached to 3 C groups

Question 22

Rank the 3 carbocation types by stability in descending order and outline why

Answer 22

Tertiary, Secondary, Primary
Tertiary most stable because alkyl group slightly release e- towards C+ (inductive e- donating)

Question 23

What determines the major and minor product of electrophilic addition?

Answer 23

The C+ stability
More stable C+ = major product

Question 24

Outline the 2 nucleophiles that react in nucleophilic addition

Answer 24

1. :CN-
2. :H-

Question 25

What type of compound reacts in nucleophilic addition?

Answer 25

Ketone

Question 26

Outline the 2 reagents that react in nucleophilic addition

Answer 26

1. Acidified KCN (aq) 2. NaBH4 (aq)

Question 27

Why does the nucleophilic addition of ketones form racemic mixtures

Question 28

Outline the mechanism steps of the nucleophilic addition between butanone and HCN

Answer 28

1. :CN- ion attacks the +δ C atom part of the C=O group. e- pair attacks the =O group forming :O- 2. The :O- ion attacks a H+ ion from the acid forming an R-OH group

Question 29

Outline the mechanism steps of the nucleophilic addition of a ketone with 2[H]

Answer 29

1. :H- ion attacks the +δ C atom bonded to the C=O group. The e- pair from C=O attacks the O atom forming :O- 2. The :O- atom attacks a H+ ion forming an R-OH group

Question 30

Outline the reagents that react in nucleophilic addition-elimination